Roman Emperor. On 20 May 1618, Klesl, who continued to promote a Catholic-Protestant rapprochement, was arrested by Ferdinand II and Maximilian III. Holy Roman Emperor Matthias died on 20 March 1619. The Bohemian estates turned against Ferdinand II, and on 26 and 27 August 1619 elected Frederick V, Elector Palatine, the leader of the Protestants in the Holy Roman Empire, as the new "winter king" of Bohemia. On the following day, Ferdinand II was elected Holy Roman Emperor by the other princes of the Kingdom of Germany. The events in Bohemia resulted in mobilization of the German Catholic League, and with Spanish support, Ferdinand II defeated the Bohemian estates and expelled the "winter king" in the Battle of White Mountain on 8 November 1620. Sources References Bibliography 1617 treaties 1617 in the Habsburg monarchy 1617 in Spain Habsburg Bohemia 1617 in law Eighty Years' War Matthias, Holy Roman Emperor Ferdinand II, Holy Roman Emperor Treaties of the Habsburg monarchy Treaties of Spain Habsburg monarchy–Spain relations